Spark-plug.



R. A. STRANAHAN.

- SPARK PLUG.

| n ILED sumo. ms.

* Patented Aug. 19,1919.

JQIMQR.

UNITED STATES PATENT OFFICE.

ROBERT ALLEN STRANA HAH, O1 TOLEDO, OHIO, ASSIGNOB. TO CHAMPION SPARK PLUG COMPANY, OF TOLEDO, OHIO, A CORPORATION OF DELAWARF SPLBK-PLUG.

, Specification 0! Letters Patent I same, reference being had to the accompanying drawings and to the characters of reference marked thcmon, which form a part of this specification. y

This invention relates to the manufacture of spark plugs and particularly tothe manner of securing the electrode terminal caps or heads to the outer ends of the porcelains carrying the same.

Considerable difliculty from the breakage of porcelains has been experienced in the manufacture of spark plugs employing porcelain insulators and having clwtrode'termina-l caps at their outer ends which fit over the outer porcelain ends and are firmly compressed at their inner edges under retaining shoulders on the porceluins, such breakage occurring from the, compressing force applied to the cap edges. Porcelains vary more or less in size and this, together with the constant positive compressing action of the cap applying nmchincs causes quite a large percentage of breakage of porcelains.

To overcome such liability to breakage the caps in some instances have been cemented on the porcelains or insulators. Such practice has been found objectionable, however, as different cements heretofore employed for the purpose have contained a fairly high percentage of moisture and when a on. and oreelain cemented together there )y are su jected to a drying treatment, the outer edge portion of the cement first dries, thereby forming an edge seal and entrapping the remaining moisture within the cap. It is found that no amount of drying will eliminate this moisture and if the baking or drying temperature is raised sufliciently high the entrapping moisture forms into steam and leaves the cement structure decidedly porous. I

The object of my mifmtion is the [m Patented Aug. 19, 1919.

Application flied September 10, 1918. Serial No. 253,366.

vision of a cement agent between the cap and porcelain of a spark plug, which agent when subjected to t e required drying or baking temperature has no tendenc to seal at the point where the lower edge 0 the cap and porcelain come together and which 0bviutes the other objection incident to the use of cements heretofore used for the pur Other advantages of the invention wi be apparent from the followin descri tion.

The invention is fully escrib in the following specification and illustrated in the accompanying "drawing, which is a central longitudinal section of a spark plug embodying the same.

In the drawing, 1 designates the customary center electrode carrying porcelain of a. spark plug, 2 the center electrode, 3 the terminal cap or head therefor, which fits over the outer end of the porcelain and is compressed at its inner edge under a retaining shoulder 4.- on' the porcelain, and 5 a. cementing agent between the porcelain and cap.

This invention consists in the use of a. cement between the cap and porcelain, which cement is not only adapted to fill any voids or spaces thercbetween and is practically free from molsture in its composition, but is also sulliclently compressible or resilient in its nature to prevent a breaka of thr porcelaiu when t a terminal cap go is forcibly compressed thereagainst and t e orcelain is slightly over size, or the edge 0 the cap of greater thickness than customarily. In such case the compressibility of the cement compensates for the variation in size. It is found that the ccmentitious compound known to the trade as bakelite is particularlyadapted for this use, and that it reduces to a minimum the breakage of porcelains in the compressing of terminal caps thereon. Bakelite is the trade name for a resinous condensation product, beingsomctimes termed condensite,' and is formed by chemically condensing together phenols and an aldehyde.

llaving thus described my invention, what I claim as new and desire to secure by Letters Patent is:-

1. Tn a spark plug, a center i-lmztrode carrying insulator, a metal terminal mombar for said nsulator, and a resinous condensation pmduct cementing said member and iusulutar togethvr.

2.1M a spark plug, a center electrode carrying nsulatur, :1 terminal cap fitting V uver an end thereof, and u resinous condensatiun Ir-oduct cementing the cap and msulatm' mgether.

ROBERT ALLEN STRANAHAN. 

